System for automatically weaning a patient from a ventilator, and method thereof

ABSTRACT

A patient ventilator system for automatically weaning a patient from a ventilator.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. Ser. No. 09/660,820,filed Sep. 13, 2000, which is a continuation of U.S. Ser. No.09/045,461, filed Mar. 20, 1998, now issued as U.S. Pat. No. 6,158,432,which is a continuation-in-part of U.S. Ser. No. 08/569,919, filed Dec.8, 1995, now issued as U.S. Pat. No. 5,931,160.

FIELD OF THE INVENTION

The invention relates generally to the field of medical ventilators or,more specifically, to the control of such ventilators.

BACKGROUND OF THE INVENTION

A medical ventilator delivers gas to a patient's respiratory tract andis often required when the patient is unable to maintain adequateventilation. Mechanical ventilation is the single most importanttherapeutic modality in the care of critically ill patients. Knownventilators typically include a pneumatic system that delivers andextracts gas pressure, flow and volume characteristics to the patientand a control system (typically consisting of knobs, dials and switches)that provides the interface to the treating clinician. Optimal supportof the patient's breathing requires adjustment by the clinician of thepressure, flow, and volume of the delivered gas as the condition of thepatient changes. Such adjustments, although highly desirable, aredifficult to implement with known ventilators because the control systemdemands continuous attention and interaction from the clinician.

Further, patients requiring ventilatory assistance must overcome airwayresistance in the breathing circuit during exhalation. This resistance,combined with the stiffness of the lungs and the thoracic cage undercertain pathological conditions, imposes a significant workload upon apatient whose reserves may already be compromised by underlying diseaseprocesses.

SUMMARY OF THE INVENTION

The invention relates to a medical mechanical ventilator device adaptedfor use in weaning a patient from mechanical ventilation. In oneembodiment, the device measures the patient's minute volume, breathfrequency, and detects a patient's spontaneous breath. The devicecompares the patient's minute volume and the patient breath rate to apredetermined minute volume and a predetermined breath rate entered by aclinician. In a pressure support mode, the device decreases patientpressure support level if the patient's spontaneous breathing rate fallswithin the predetermined range of breathing and the patient's minutevolume exceeds the predetermined minute volume. In one embodiment, thepatient's spontaneous breathing rate and the patient's minute volume isdetermined on a breath-by-breath basis. For the purposes of thisinvention, intrabreath is defined as within the period of one breathcycle, and interbreath is defined as within the period of at least twobreaths.

In another embodiment, the invention is a ventilator system adapted foruse in weaning a patient from mechanical ventilation. The ventilatorsystem comprises a pressure source in communication with the patient'srespiratory system to provide pressure support to the patient. Thedevice further comprises a breath frequency monitor, a minute volumeflow meter, an input device, and a data processing unit. The dataprocessing unit compares the patient's breathing frequency and patient'sminute volume to the breathing frequency and minute volume entered bythe clinician. Pressure support is adjusted by the ventilator on anintrabreath or interbreath basis.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of a ventilator of theinvention.

FIG. 2 is a detailed block diagram of a display controller.

FIG. 3 is a detailed block diagram of an embedded controller.

FIG. 4 is a detailed block diagram of a ventilator pneumatic unit.

FIG. 5 is a diagram illustrating an embodiment of the adjustment ofnegative pressure applied to a patient as performed by an embodiment ofthe invention.

FIG. 6 is psuedocode of an embodiment of a triggering algorithm used bythe ventilator of the invention.

FIG. 6 a is a pressure and flow diagram of the patient airway gas flowand patient airway pressure used by the algorithm of FIG. 6 to determinepatient ventilation triggering.

FIG. 7 is an illustration of a display screen when the ventilatorcontrol system is in the operational mode.

FIG. 8 is an illustration of a section of the display screening showinga minute volume wheel.

FIG. 9 is an illustration of a section of the display screening showinga control slider.

FIG. 10 is an illustration of a section of the display screening showinga numerical controller.

FIG. 11 is a flow chart of the data structure hierarchy employed by theventilator control system.

FIG. 12 is an embodiment of a flow chart of an exhalation assistalgorithm executed by an embodiment of the invention.

FIG. 13 is an illustration of a simulation mode display screen for theventilator control system.

FIG. 14 is a functional block diagram of the simulator portion of theventilator control system

FIG. 15 is an illustration of a section of the display screening showinga waveform shaper.

FIG. 16 is an illustration of a therapy programming screen for theventilator control system.

FIG. 17 is a flow chart for automatic weaning of a patient from aventilator according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

1. Ventilator Control System—The invention features a ventilator controlsystem for controlling a ventilator pneumatic system in a medicalventilator. The ventilator control system provides a clinician withcomplete control of a patient's airway flow and pressure throughout therespiratory cycle, and thereby enables the clinician to determine theoptimal therapy for the patient. In order to decrease the work ofexhalation in this situation, negative pressure can be applied to theexhalation circuit of the patient's ventilator to reduce the resistanceto airflow.

Because resistance to airflow is an exponential function of flow,negative pressure must be adjusted to compensate for resistance asincreases and decreases in airflow and airway resistance occur. If toomuch negative pressure is applied to the conducting airways dynamiccollapse of the conducting airways can occur and this may result inalveolar gas trapping. Varying the applied negative pressure accordingto airflow and airway resistance allows maximum assist to be appliedduring peak expiration, when resistance and work of breathing isgreatest. By decreasing the applied negative pressure at lower airflowrates, airway collapse can be averted.

If airway pressure rises above the clinically indicated level ofpositive end-expiratory pressure (PEEP), the lung will beoverpressurized thus the effective airway pressure throughout theexpiratory cycle is titrated throughout the expiratory phase underprecise algorithmic control. The clinical benefit of a certain PEEPlevel will be diminished. Thus, the effective airway pressure throughoutthe expiratory cycle must remain greater than zero and less than PEEP.

FIG. 1 is a block diagram of a ventilator including a ventilator controlsystem 10 incorporating the features of the invention. The ventilatorcontrol system 10 includes a display controller 12 and an embeddedcontroller 14. The display controller 12 provides an interface to theclinician 16, and the embedded controller 14 provides an interface witha ventilator 17 providing ventilation to a patient 20. The displaycontroller 12 and the embedded controller 14 each include memory (notshown) and are electrically coupled via a shared memory interface 15.Data from the display controller 12 and the embedded controller 14 arestored in a database 13.

A sensor monitoring system 19, including an exhalation flowmeter 11 acircuit resistance sensor 9 and a pressure sensor 7 in communicationwith the airway 21, provide signals to a embedded controller 14 relatingto airway pressure, flow and resistance. These measured values arestored in a database 13. These values are also compared with valuespreselected by a user by way of the embedded controller 14 to calculatethe amount of negative pressure to be generated in the ventilator 17 inorder to produce an airway pressure greater than zero and less thanpositive end-expiratory pressure. A pneumatic system 41 regulates theflow of gas delivered from the source of pressurized gas 45 through aVenturi valve within the ventilator 17 to produce this negativepressure. One embodiment of such a pneumatic system 41 is described inU.S. Pat. No. 5,664,563, owned by the assignee of the present invention,incorporated herein by reference. A pressure sensor 51 measures theamount of negative pressure produced within the ventilator 17 andtransmits these data to the embedded controller 14. These data arestored in the database 13 and displayed on the display 24 of the displaycontroller 12.

Initially, the clinician 16 enters target values into the system 10 byway of the input device 26 of the display controller 12. Each of thesetarget values is compared with a corresponding current value ofventilatory unit pressure, airway pressure, airway flow and airwayresistance by the embedded controller 14. Upon determining that there isa difference between current pressure, flow and resistance values andthose values entered by the clinician 16, the embedded controller 14generates a signal to the pneumatic system 41 so that the pneumaticsystem 41 changes the amount of negative pressure produced by theventilator 17. The ventilator 17 is in pneumatic communication with aflexible tubing 21 capable of attachment to a patient 20. The clinician16 can also directly adjust the pneumatic system 41 by manipulating aplurality of controls on the input device 26 of the display controller12.

The clinician 16 enters numerical data at the display controller 12relating to the desired level of airway resistance in the flexibleairway tubing 21 or relating to the desired amount of negative pressurein the pneumatic system 41. These entered values signal the pneumaticsystem 41 to change the amount of negative pressure on a per breathbasis within the pneumatic system 41 until the pressure in the pneumaticsystem 41 or the resistance in the airway tubing 21 equals the valueentered by the clinician 16.

The pneumatic system 41 controls gas flow and pressure in the patient'sairway using a patient circuit. An electromechanical fresh gas flowcontrol and measurement system provides a metered blend of oxygen andair via a heated, humidified gas delivery system. A high speedpneumatically driven, electronically controlled proportional valve anddual Venturi system provides bi-directional flow and pressure control asdescribed in U.S. Pat. No. 5,664,563 incorporated herein by reference.Pressure 7 and flow 11 sensors provide feedback control of the desiredbreathing pattern and verify operation within safe limits. The pneumaticand electronic systems and patient circuit are described in extensivedetail in commonly assigned patent application Ser. No. 08/352,658,incorporated herein by reference.

The safe performance of the ventilator 10 is enhanced by the redundancyof the two independent display controller 22 and embedded controller 30processors, which continually check each other's performance via theshared memory interface 15. The embedded controller 14 communicates itsstatus, and that of the patient, to the display controller 12. Theembedded controller 14 maintains a non-volatile record of the therapycontrol structure and continues to operate at the last known goodsettings if communication becomes lost. The two systems which comprisethe ventilator control system 10 give both audible and visual messageswhen an alarm condition exists, and maintain an alarm history. Thesystems provide alarms and mandatory patient support upon detection ofapnea (i.e., the detected absence of breathing). During operation, bothsystems perform background tests to detect system faults. The ventilatorprovides a series of reduced operation modes to provide life support ifsystem capability is compromised.

In more detail, FIG. 2 is a block diagram of the display controller 12.The display controller 12 includes a processor 22, a display 24 and aninput device 26. In one embodiment, the input device 26 is a touchscreenused in conjunction with the display 24. The processor 22 collects inputinformation from the clinician 16, validates the input, creates atherapy control structure from the input information and sends theresulting structure to the embedded controller 14. The therapy controlstructure is a hierarchical arrangement of similar data structures whichincludes one or more mode control structures, one or more breath controlstructures, one or more phase control structures and one or more cyclecontrol structures. Data generated and collected by the processor 22 arestored in the database 13. The display 24 maintains and displays thepatient's history in a graphical format which highlights the patient'sstatus. In one embodiment, the display 24 is a CRT. In anotherembodiment, the display 24 is a flat panel display. More specifically,the display 24 provides a visual indication of the current breathcontrol parameters, alarm and fault conditions, and the current statusof the patient's pulmonary system, including gas pressure, flow andvolume. In one embodiment, the touchscreen 26 covers the surface of theCRT display 24 and provides a straightforward, highly flexible means tochange control settings.

The display controller 12 is a powerful graphics workstation withhardware and software components. In one embodiment, the clinicianinteracts with the display controller 12 via a color CRT monitor 24 anda touchscreen 26. The display 24 is modified to run from an isolatedpower supply, and the touchscreen power supply and controller are builtin to the monitor. In one embodiment, the processor 22 is included in asingle board computer which also includes RAM, an integrated high speedgraphics driver, and an integrated dual port memory. The displaycontroller 12 also includes a hard disk drive 23.

While the display controller 12 provides interpretation and decisionsupport information on the display 24, the ventilator 17 does not changeany breath control parameters unless directed by the clinician 16.Nevertheless, the display controller 12 provides a flexible userinterface with multiple interactive levels, from simple text menus ofcontrols for inexperienced users, to complete visual feedback forclinicians who understand the patient models and can intervene moreaggressively and effectively.

In more detail, and referring also to FIG. 3 a block diagram of theembedded controller 14 is depicted. In one embodiment, the embeddedcontroller 14 includes a system board 28, a real time data processor 30,a ventilator processor 32 and an airway processor 31. The real timeprocessor 30 manages sensor data collection from the sensor monitoringsystem 19, processes measured data, performs alarm/fault detection andprovides control data to the ventilator 17. The embedded controller 14further receives data input by the clinician 16 and accesses with thedatabase 13.

A first data processor 31, an airway processor, receives signals fromthe patient sensor monitoring system 19 relating to airway pressure,flow and resistance. A second data processor 32, a ventilatory unitprocessor, receives signals from the pressure sensor 51 in communicationwith the ventilatory pneumatic system 18. Signals from both dataprocessors 31 and 32 are transmitted to a third data processor, a realtime data processor 30. This data processor 30 calculates the amount ofnegative pressure that must be generated by the pneumatic system 41 tochange the airway resistance to exhalation. This calculation is made bycomparing the data relating to airway pressure, flow and resistance topreselected values and then calculating the change in ventilatory unitnegative pressure required to affect the desired change in airwayresistance.

In more detail, and referring also to FIG. 4, a block diagram of theventilator 17 in communication with the flexible airway 21 that is theconduit for inhalation from the patient 20 is depicted. The pneumaticsystem 41 regulates the amount of negative pressure produced within arigid chamber 43 by adjusting the flow of gas from a source ofpressurized gas 45 through a Venturi valve 47. Within the rigid chamber43 is a flexible canister 49. Negative pressure produced within therigid chamber 43 is transmitted to the flexible canister 49 and thus tothe patient airway 21 which is in pneumatic communication with theflexible canister 49. In this way, negative pressure is applied to thepatient airway 21 to assist the patient's exhalation through thecanister 49 into the medical ventilator 7. Pressure within the flexiblecanister 49 is measured by a pressure sensor 51. These data aretransmitted to the embedded controller 14.

Now referring also to FIG. 5 a detailed functional block diagram of theventilator control system 10 is depicted. As shown, the clinician 16manipulates a control setting slider 34 to change or set one or morebreath parameters. A change alert panel 36 on the display 24 informs theclinician 16 of the process, from input to implementation, to assure himthat his input information is being processed properly. As notedpreviously, a change to one or more breath parameters will lead tochanges in one or more data structures of the therapy control structurehierarchy. It is noted that FIG. 5 provides an example of a breathparameter change which results in a change at the level of the breathcontrol structure. The validation process includes the processor 22validating 38 the clinician's inputs and creating 40 a breath controlstructure which is stored in memory. The display controller 12 transmitsthe breath control structure to the embedded controller 14 and informsthe clinician 16 of successful transmission via the change alert panel36. The embedded controller 14 initially stores 44 the breath controlstructure in local memory. The embedded controller 14 re-validates 46the settings within the breath control structure. The embeddedcontroller 14 implements 48 the validated breath control structure 48using a breath control algorithm 50 and provides signals to thepneumatic system 41 for simultaneously changing one or more controlsettings at the appropriate time. This process enables the user tochange or implement a new therapy so that the therapy delivered to thepatient is essentially uninterrupted, and the new therapy issynchronized with the next inspiration. If, however, any step in theprocess is not completed, the clinician is alerted via the panel 36 tothe cause of the error and the process is terminated.

The ventilator control system 10 provides two independent feedback pathsto assure the clinician 16 that his setting change has been properlyimplemented. First, the embedded controller 14 calculates a series ofbreath monitoring values and sends them to the display controller 12,where the values are displayed 60 contiguous to the desired settingcontrols. The breath monitoring values can be, for example, set breathrate, measured breath rate, set tidal volume, measured inhaled volume,and measured exhaled volume. The display controller 12 also displays 60a series of measurements (e.g., peak airway pressure, peak airway flow,and PEEP) from the waveform data both numerically and graphically.Second, the display controller 12 displays 54 the continuous waveformson the display 24. The waveforms are derived 56 from raw data from thesensors 19, returned from the embedded controller 14 and passed directlyto the display 24.

One feature of the ventilator control system 10 is that it can beconfigured to provide an assisted phase of a breath to the patient 20.As noted previously, the accumulated volume of gas inhaled by thepatient as a result of his spontaneous respiratory muscle activity canbe monitored. To accomplish this, the sensor monitoring system 19measures the flow of gas inhaled by the patient 20 at the beginning ofthe inspiration phase of the breath and integrates the flow to providethe measured volume. The embedded controller 14 compares the measuredvolume to a trigger volume set by the clinician 16, and adjusts theplurality of controls within the pneumatic system 41 when the measuredaccumulated volume exceeds the trigger volume to provide an assistedphase of a breath. The embedded controller 14 also may adjust thetrigger volume dynamically according to measured patient flow andpressure signals indicating the phase of the respiratory cycle. Inparticular, the embedded controller 14 may increase the trigger volumeset by the clinician 16 during periods of the breath where increases inthe pressure at the airway of the patient 20 may be induced by changesin the pneumatic system 41, and not by spontaneous efforts of thepatient.

Another feature of the ventilator control system is its ability todistinguish between active inspiratory effort and passive reverseairflow due to the elastic rebound of the chest wall and lungs. Thepresent system is configured such that if the patient's spontaneousinspiratory efforts are being assisted, passive reverse airflow can noterroneously trigger an assisted breath. To accomplish this pressure andflow data provided by the sensor monitoring system 19 are analyzed bythe imbedded controller 14 to discriminate between passive airflow andactive initiation of inspiration. Specifically, referring to FIGS. 6 and6 a, the clinician sets the trigger volume needed to initiate a breath.The system 10 then determines the baseline pressure and flow for thepatient.

As the patient exhales, the system 10 monitors both the patient airwayflow and the patient airway pressure. Referring to FIG. 6, if the gasflow is seen to flow into the patient, and the pressure slope ispositive, the flow into the patient is considered to be a result ofchanges in the pneumatic system and no inhalation is triggered (FIG. 6a). If the pressure decreases and the gas flow is into the patient (Step300), then the total amount of gas inhaled by the patient is measured,and compared to the trigger volume (Step 310).

If the total amount of gas inhaled is greater than the trigger volumeand this value has been reached in less than 200 msec, a breath isinitiated. If the trigger volume has not been reached and it is takingmore than 200 msec, the volume of inhaled gas is continued to bemeasured until the trigger volume has been reached (Steps 320, 330).

Another feature of the ventilator control system is its ability tocompensate for gas flow resistance into and out of the lungs of thepatient 20. Using the input device 26, the clinician 16 can set aresistance parameter of the patient's respiratory system to a selectedvalue. Alternatively, the display controller 12 may calculate a valuefor the gas flow resistance from gas flow and pressure measurementsprovided by the sensor monitoring system 19. The gas flow resistance isdescribed by the equation::Gas Flow Resistance=(Inspiration Peak Pressure−End Inspiration PlateauPressure)/(Inspiration Flow at Peak).The selected or calculated resistance value is provided to the embeddedcontroller 14 by the display controller 12. The embedded controller 14adjusts one or more controls of the pneumatic system 41 to compensatefor the resistance to flow. The compensation for resistance to flow maybe selected to occur during any one or more of the inspiration,exhalation or post-breath phases of a breath. Further, the controls maybe adjusted to compensate for different selected or calculatedresistance during different phases of a breath.

2. Display Controller—The display controller 12 is an intelligentassistant for the clinician 16. The display controller 12 quicklyinforms the clinician 16 of the effects of intervention, provides fast,graphical feedback, and presents information in a manner that requiresminimal training to understand.

Referring also to FIG. 7 an illustration of a display screen 64 providedby the display controller 12 is depicted. The display controller 12 usessoftware-generated waveforms and software-generated icons for controland alarms settings. The bottom row of touch sensitive on/off buttons 66includes: a Power button that controls the ventilator control system; aFreeze button to pause the display; a Modes button to display variousmodes; a History button to play back a database of historical patientprotocols; a 100% O₂ button to flush the ventilator with oxygen; Helpand Save buttons; and an Others button to display other capabilities.

The left side of the screen includes a list of the publicly availableventilator control settings. The top area displays the current mode ofventilation 67 (e.g., Backup). Below the current mode display, each rowin the list has three columns. The left column is the current set value.If a row in the left column is inactive, it displays an OFF indication.Important current set values are highlighted. The middle column is atouch sensitive display showing the abbreviated title of the setting.The right column is the actual value of the setting as measured duringthe previous breath. If the actual value exceeds an alarm limit, theexceeded value turns red and a large alarm message is displayed on thescreen. By touching a row, a control slider (not shown) appears on theright side of the screen. The control slider enables the clinician tochange various parameters (e.g., alarm levels, control settings) and isdescribed in detail below.

The middle area of the display screen is divided into top and bottomregions (70, 72). The bottom region 72 can include a variety of virtualinstruments including: additional user-defined waveforms, trendlines, anevents log, measured minute averages and other options. The top region70 includes real time airway flow and pressure waveforms (74, 76), whichare displayed over different shades of gray to indicated the breathphase. The airway flow waveform 74 illustrates flow into the patient, orinspiration (positive flow), and flow out of the patient, or exhalation(negative flow). The pressure waveform 76 illustrates that the patient'sairway rises above ambient for inspiration and falls during exhalation.The waveforms are tracked by a cursor that can be programmed to follow apeak, average, plateau or manually set position. The waveforms aredisplayed in fixed axis, moving erase bar format. The time axisresolution is user adjustable and displays time in seconds. Overwritingof the display starts at the beginning of an inspiration, so that thefirst displayed breath starts at a fixed point on the screen. Thevertical axes are scaled to keep the displayed waveforms and settings inclear view.

The right side 77 of the display screen normally includes a flow-volumeloop 78, a pressure-volume loop 80 and a minute volume wheel 82. Acontrol slider and other optional panels can overlay this side when auser so desires. The flow-volume loop 78 is updated each breath to showthe timing of delivered airflow. The vertical axis of the loop shares acommon range and alignment with the airway flow waveform 74. Thepressure volume loop is updated each breath to show the condition of thelungs. The vertical axis of the loop shares a common range and alignmentwith the pressure waveform 76. Calculated resistance and compliance arealso displayed.

The minute volume wheel 82 provides a comprehensive summary of thepatient's breathing for the last minute. The minute volume wheeldisplays a wealth of historical breath information (e.g., minute volume,inspiration phase, exhalation phase, inspiration/exhalation ratio,breathing rate, spontaneous minute volume, inhale tidal volume, exhaletidal volume, leakage) on a single integrated graphic circle so that theclinician can readily evaluate ventilation during the last minute.

Referring to FIG. 8, a minute volume wheel 84 represents one minute ofventilation as a circle with an area corresponding to measured minutevolume. The measured minute volume is represented numerically, as thecenter number, and graphically, as a circle 86 drawn over a backgroundcircle 88 that has an area corresponding to the target minute volume.When the measured minute volume is exactly equal to the target minutevolume, the two circles are blended in color and appear as one circle.When the measured volume is larger than the target volume, thebackground circle bleeds through and is visible. When the measuredvolume is smaller than the target volume, an uncovered portion of thebackground circle is visible.

One minute of ventilation is drawn as a circle 90, one wedge at a time,and is redrawn once a minute. Like the face of a watch, each degree ofthe circle 90 corresponds to one sixth of a second. Each inspiration isdrawn as a wedge 92 with an area corresponding to delivered volume. Thiswedge is drawn over an inspiration spoke 94 that extends to maximumminute volume. Each exhalation is drawn as a wedge 96 with an areacorresponding to exhaled volume. This wedge is drawn over an exhalationspoke 98 that extends to maximum minute volume. The spokes indicatebreathing regularity and inhale to exhale (I:E) time ratio, and thewedges indicate tidal volumes. Difference between the radius ofinspiration and exhalation wedges indicates the I:E ratios. The I:Eratio and breathing rate are also represented numerically (100, 102).The pairs of inspiration and exhalation wedges are coded by color toindicate spontaneous breaths, those triggered and partially controlledby the patient, and mandatory breaths, those triggered and controlled bythe ventilator. The ratio of the colored areas indicates the ratio ofspontaneous to mandatory breathing during the minute just past.

Referring, again to FIG. 7, the display controller provides a method forclinician control of the displayed waveforms. Each waveform (74, 76) iscontinuously measured and displayed on a background that changes colorto indicate the phase of a breath. The rectangular area 200 for anyphase of the waveform (74, 76) is used as a target for the touchscreen.When the clinician selects a phase of a waveform, the display controllerdisplays the associated ventilator controls for available for adjustmentby the clinician.

The display controller provides cursors 201 which are actually floatingwindows. More specifically, windows of one or two pixels width floatover the waveforms (74, 76), thereby creating cursors 201. Since thecursors are independent of the background waveform graphics, numerousadvantages result including drawing optimization, dynamic repositioningbased on changing waveform values, positioning based on user interfacegestures.

The background of the waveform (74, 76) includes color shading toindicate breath phase, title, units and scale information. Redrawingthese graphics as new waveform samples are displayed generally requiressubstantial computer time, and the display controller performs thisfunction efficiently notwithstanding the complexity of the backgroundimage. To perform this task efficiently, background images are createdonce. A narrow rectangular region 202 is removed from these images andpasted in front of the moving waveform to clear out the previouswaveform and refresh the background prior to the new waveform. The widthof the rectangular area 202 is kept sufficiently small so that therefresh is smooth in appearance. The x-axis coordinate of the currentwaveform position is used to control the x-axis position from which toremove a strip of background image. Multiple color coded backgroundimages can be maintained (e.g., three gray shades for the breath phases)and images removed from the desired one depending on the state of thewaveform.

By selecting one of the control buttons on the touch display, theclinician 16 can display the control slider 106 for the control settingin a fixed location at the right of the screen, as shown in FIG. 9. Ascroll bar title 108, located near the top of the slider 106, indicatesthe name of the control setting. The full vertical range 108 indicatesthe allowed set limits. The center slider indicates the current position110 and the range 112 of the control setting. The upper and lowersliders (114, 116) indicate the current alarm limit settings. Theposition 110 of the current setting within the allowable range 112 andwithin the alarm limits (114, 116) is readily apparent to the clinician.The clinician can move any of the sliders to change the set values insteps of approximately 1% of the allowable range, or with the “Exact”button selected, approximately ten times more precision (i.e., about0.1% of the allowable range). When the desired value is reached, theclinician depresses the Accept Changes button to change the parameter.

Alarm settings are matched with control settings in the appropriatecontrol sliders. Some control settings have two associated alarms,others have only one associated alarm or do not have any associatedalarms. For example, both high and low inspiratory pressure alarms areprovided on the Airway Pressure control slider. If an alarm limit isexceeded during operation, the alarm is displayed in an alarm window,and an audio alarm turns on. Alarms are non-latching, i.e., the alarmindication turns off when the detected level no longer violates the setlimit. Available control settings and ranges, alarm settings and ranges,and measured parameters are listed in the following table: ControlSettings Tidal Volume (Compliance Compensated) 50 to 2000 mL BreathingRate 2 to 150 bpm Peak Inspiratory Flow (BTPS Compensated) 10 to 120L/min Oxygen Percentage 21 to 100% Peak Inspiratory Pressure 2 to 120cmH₂0 Exhalation Assist 0 to 30 cmH₂0/L/sec PEEP 0 to 20 cmH₂0Inspiratory Time 0.2 to 4 sec Inspiratory Pause Time 0 to 1 secSensitivity (Patient Effort Trigger) 0 to 250 mL Flow Drop-OffPercentage (Percent of Peak) 5% to 80% Humidifier Temperature 30 to 60°C. Airway Temperature 15 to 40° C. Waveform Shape (clinician modifiable)custom, square decelerating, modified fine Monitored and DisplayedParameters Exhaled Tidal Volume (Compliance 50 to 2500 mL Compensated)Measured Breathing Rate 2 to 150 bpm Peak Inspiratory Flow (BTPSCompensated) 10 to 120 L/min Oxygen Percentage 21 to 100% PeakInspiratory Pressure 0 to 120 cmH₂0 PEEP 0 to 20 cmH₂0 Mean AirwayPressure 0 to 120 cmH₂0 Inspiratory Time 0.1 to 4 secInspiratory:Expiratory Ratio 0.1 to 10.0 Minute Ventilation - Controlled0 to 99 L/min Minute Ventilation - Spontaneous 0 to 99 L/min AirwayTemperature 15 to 40° C. Lung Compliance 10 to 150 mL/cmH₂0 AirwayResistance 1 to 60 cmH₂0/L/s Leak 0 to 20 L/min Airway Flow Waveform−120 to +120 L/min Airway Pressure Waveform −20 to +60 cmH₂0 Flow-VolumeGraph, Pressure Volume see text Graph Fresh Gas Flow Bar Graph see textMinute Volume Wheel see text Alarms and Indicators High/Low ExhaledTidal Volume Alarm 50 to 2000 mL High/Low Respiratory Rate Alarm 2 to150 bpm Low Oxygen Fresh Gas Flow Automatic, % O₂ dependent Low AirFresh Gas Flow Automatic, % O₂ dependent Low Oxygen Supply PressureAlarm 25 psig High/Low Airway Pressure Alarm 2 to 120 cmH₂0 High/LowInspiratory Time Alarm 0.2 to 4 High/Low Inspiratory:Expiratory RatioAlarm 0.1 to 4.0 High/Low Minute Volume Alarm 1 to 40 L/min Airway LeakAlarm 1 to 20 L/min Patient Disconnect Alarm Automatic ApneaAlarm/Backup Ventilation 30 Internal Battery Notification Alarm Batteryin Use % Remaining Pneumatic System Fault Alarm Automatic Alarms Silence120 High/Low Oxygen Alarm 18-100% O₂

In one embodiment, the display screen 24 is covered by a resistivetouchscreen. Known touchscreen interfaces require that the user touch agraphic object on the screen, but this action generally obscures theobject. The touchscreen interface of the present invention defines anarea whose shape, size and position is dynamically computed based on thecharacteristics of the associated graphic object. The interfaceinterprets touching by the user as a manipulation of the associatedgraphic object. More specifically, a dragging motion moves theassociated object, or change its value or other attributes.

Referring again to FIG. 9, the display controller includes software formanipulating the characteristics of the breath parameter Airway Pressure106 displayed in the control slider 104 on the touch-sensitive display24. When the clinician 16 selects a control button to display thecontrol slider 106 for Airway Pressure, the display controller 12dynamically defines a touch zone on the touch-sensitive display. Morespecifically, touch zones are defined for each slider (i.e., high alarm,low alarm, position and allowable range) within the control slider. Eachtouch zone is slightly larger than the displayed slider. By way ofexample only, the touch zone for high alarm may extend into regions 118to either side of the color coded high alarm region 114. The displaycontroller 12 receives a touch signal when the clinician 16 touches anylocation within the touch zone and changes the range of the high alarmslider breath parameter in response to the touch signal. In other words,the display controller 12 increases the high alarm limit in response tothe clinician 16 touching a location within the region 118 and dragginghis finger in a upward path. Because his finger does not obscure thehigh alarm limit, the clinician can actually see the limit being changedas it happens.

Referring also to FIG. 10, the display controller 12 includes softwarefor providing precise numerical control without the requirement of akeyboard. The display controller 12 displays a window 120 that lookslike a numeric text field, but has a background color to distinguish theleft region 122 from the right region 124, relative to the decimalpoint. Once either numeric region 122, 124 has been touched, a largertouch sensitive area 126, 128 respectively is associated with each ofthe numeric regions. When the clinician 16 touches a touch sensitivearea and moves in a vertical path, the interface provides continuousnumeric feedback by increasing or decreasing the displayed value.

3. Embedded Controller—Referring again to FIG. 1, the embeddedcontroller electronics 14 is based around microprocessors 31, 32. Themicroprocessor 32 is in electrical communication with the ventilatoryunit 17 and the microprocessor 31 is in electrical communication withthe sensor monitoring system 19. The embedded controller relies onindustry standard bus based modules to perform certain functions andcustom printed circuit boards to perform other functions. The modules,the printed circuit boards, the ventilatory unit pressure processors 32and the airway processor 31 are mounted on or connected to on a mainprinted circuit board 28. A real time operating system is the foundationof the embedded controller software, which runs the algorithms requiredfor measurement and control. A power system converts line power andprovides battery backup for a average of one hour. The embeddedcontroller 14 has microprocessor and associated input/output hardware toprovide for closed loop control of pneumatic system 41 and theacquisition of patient data. The embedded controller 14 communicates thestatus of the patient and its own status to the display controller 12.The embedded controller 14 responds to commands and setting changesreceived from the display controller 12, and maintains a non-volatilerecord of instrument settings to maintain operation in the absence ofboth communication from the display controller and line power.

The embedded controller 14 performs real time data acquisition of twentythree different analog input signals including:  1. Flow Oxygen,  2.Flow Air,  3. Flow Third Gas,  4. Flow Canister,  5. Flow Exhaust,  6.Pressure Patient Airway,  7. Pressure Canister,  8. Flow Low Exhaust, 9. Temperature Airway, 10. Temperature Humidifier, 11. Voltage Battery,12. Current 5 Volts, 13. CO₂ Airway, 14. Voltage ECG, 15. Voltage QRS,16. Temperature Patient Temperature 2, 17. Pressure Patient Pressure 1,18. Pressure Patient Pressure 2, 19. Signal PT34, 20. Voltage Aux 1, 21.Voltage Aux 2, 22. Voltage Aux 3, 23. Voltage Aux 4.

The embedded controller 14 also monitors six switches: 1. PressureOxygen, 2. Pressure Air, 3. Pressure Third Gas, 4. Pressure SafetyValve, 5. Voltage Power Switch, 6. Voltage No AC Line.

The embedded controller controls nine digital outputs: 1. SolenoidExhaust Flow Zero, 2. Solenoid Canister Flow Zero, 3. Solenoid SafetyValve, 4. Solenoid Direction (I/E), 5. Heater Canister, 6. Heater FreshGas Tube and Humidifier, 7. Power CRT Display, 8. Alarm Beeper, 9.Battery Backup.

The embedded controller 14 controls four duty cycle modulated digitaloutputs: 1. Flow valve Canister, 2. Flow valve Air, 3. Flow valveOxygen, 4. Flow valve Third Gas.

The embedded controller 14 communicates with the display controller 12via a shared memory interface 15 at a data transmission rate exceeding100K bytes per second.

4. Data Structures—This section describes the architecture for softwareutilized in the embedded controller and shared with the displaycontroller. The architecture of the software is built around theconcepts of therapy controls, mode controls, breath controls, phasecontrols and cycle controls. A data structure driven state machinedetermines the control parameters for each therapy control, modecontrol, breath control, phase control, cycle control and exhalationassist.

Referring to FIGS. 1 and 11, the figures illustrate the data structurehierarchy for the ventilator control system. Using an input device 26such as the touch-sensitive display 24 within the display controller 12,a clinician can change ventilation control settings to create a newtherapy comprising a therapy control structure 140. The settings arevalidated by the display controller 12, placed into a new therapycontrol structure and sent to the embedded controller 14. The embeddedcontroller 14 validates the settings again and checks the integrity ofthe new structure before the new therapy control is accepted. Also, theclinician 16 may simulate the behavior of the new therapy control usinga simulator and may allow others to utilize the therapy control byadding it to the database 13. In any case, the clinician 16 sends thenew therapy control structure to the memory for use by the embeddedcontroller 14 in controlling the pneumatic system 41. A therapy controlstructure 142 (or a mode control) 140 is defined as a collection of modecontrol structures 142 and mode switching rules 144. A mode controlstructure (or a breath control) is defined as a collection of breathcontrol structures 146 and breath switching rules 148. A breath controlstructure 146 (or a phase control) is defined as a collection of phasecontrol structures 150 and phase switching rules 152. A phase controlstructure 150 (or a cycle control) is defined as a collection ofventilator control settings 154 and an array of waveform samples 156.Phase definitions and requirements for transitions between phases aretied directly to measurable system performance, and correlate closely topublished descriptions of the desired behavior of mechanicalventilators.

More specifically, the therapy control structure 140 is a nestedhierarchy of increasingly complex control structures. A cycle (e.g., a 4msec time slice) occurs within cycle control, which occurs within phasecontrol, which occurs within breath control, which occurs within modecontrol, which occurs within therapy control, which is the clinicallyspecified therapy that drives the ventilator pneumatic system 41. Onceeach cycle, ventilation control moves from one control state to anothercontrol state.

After each cycle, when the hierarchy of rules is tested and the state isset for the next cycle, a new therapy control structure 140 may cause abranch to the first cycle of the first phase of the first breath of thefirst mode of ventilation within the new therapy control structure, orthe new therapy control structure may be delayed a few cycles untilbetter patient synchrony can be achieved. Within a therapy, there is acollection of mode control structures 142 and a collection of rulesspecifying how and when to switch from one mode of ventilation toanother one. Thus, a therapy may define several different modes ofventilation and mode switching rules 144 for the transition from onemode of ventilation to another.

After each cycle, when the hierarchy of rules is tested and the state isset for the next cycle, the mode switching rules 144 may cause a branchto the first cycle of the first phase of the first breath of anothermode of ventilation within the therapy control structure 140. Within amode, which is within a therapy, there is a collection of breath controlstructures 146 and a collection of breath switching rules 148 specifyinghow and when to switch from one breath type to another breath typewithin the same mode. Thus, a mode of ventilation may have severaldifferent types of breaths defined, and rules specified for how to gofrom one breath type to another.

After each cycle, when the hierarchy of rules is tested and the state isset for the next cycle, the breath switching rules 148 may cause abranch to the first cycle of the first phase of another type of breathwithin the mode. Within a breath, within a mode, within a therapy thereis a collection of phase control structures 150 and a collection ofphase switching rules 152 specifying how and when to switch from onebreath phase to another phase within the same breath. Thus, a breathtype may have several different phases defined, and rules specified forhow to go from one breath phase to another. For example, breathinggenerally proceeds from an inspiration phase to a pause phase to anexhalation assist phase to a PEEP phase, but these phases may be furthersubdivided for a finer granularity of control.

After each cycle, when the hierarchy of rules is tested and the state isset for the next cycle, the phase switching rules 152 may cause a branchto the first cycle of the next phase within the breath type. Within aphase, within a breath, within a mode, within a therapy, there is aventilator control setting structure 154. This structure contains anarray of samples that comprise a specified waveform shape. During eachcycle, the control logic is driven by the waveform sample specific forthe cycle, and by a collection of ventilator control settings 154specific for the phase. The cycle time is in milliseconds, and iscurrently set to four milliseconds.

After performing all ventilation control for the cycle, the hierarchy ofrules is tested and the state is set for the next cycle, which is bydefault the next cycle within the current phase, current breath type,current mode of ventilation and current therapy. However, higher levelrules may cause a change in breath phase, breath type, mode ofventilation, or an entirely new therapy may be specified by theclinician and take control at the next cycle.

Each ventilator control setting structure 158 contains necessary andsufficient information to control one parameter of ventilation,including whether there is a high alarm level, whether the high alarm isactive, whether there is a control level, whether the control is active,whether there is a low alarm level, whether the low alarm is active,whether there is a range level, whether the range is active, and a rangetarget control structure to define how and why the parameter is to beadjusted automatically within the specified range. Each phase controlstructure has its own collection of ventilator control settings,although in practice, phases within a breath generally share the samecollection.

The data structure-driven architecture described above enhances safetyand reduces the likelihood of hazardous conditions by permittingnon-programmers to review and understand the function of the ventilatorcontrol system.

Several breath control structures are predefined in the embeddedcontroller. These breath control structures are used when hazards aredetected, such as apnea or patient circuit disconnect. They are alsoused to support the patient if the communication link between thedisplay controller 12 and embedded controller 14 is lost. Also, theembedded controller 14 checks the integrity of every therapy controlstructure sent by the display controller 12. If a requested change isinvalid, the embedded controller 14 continues operation with the lastknown valid therapy control structure. If no valid therapy controlstructure has been received, the embedded controller 14 uses thepredefined breath control structures to continue patient support.

FIG. 12 is a flowchart of an embodiment of an algorithm executed by theexhalation assist device embodied in FIG. 1. The algorithm begins withthe clinician 16 entering the desired values relating to airwayresistance or negative pressure in the ventilatory unit (Step 1). Thesevalues are then compared with data relating to airway resistance ornegative pressure in the ventilatory unit that have been measured orcalculated by the data processing unit (Step 2). It is then determinedwhether these sets of data are equal to each other or are within apredetermined range of each other (Step 3). If these values are equal orwithin a predetermined range, airway flow is then measured (Step 5). Ifthese values are not equal or within a predetermined range, the appliednegative pressure is adjusted (Step 4), and then the airway flow ismeasured (Step 5). After airway flow is measured, it is determinedwhether the measured airway flow is a positive or a negative number(Step 6). If airway flow is positive, indicating that inspiration isoccurring, a new measurement of airway flow is obtained (Step 5). Ifairway flow is negative, indicating that exhalation is occurring, airwaypressure is measured (Step 7). It is then determined whether airwaypressure is greater than zero and less than PEEP (Step 8). If airwaypressure is greater than zero and less than PEEP, airway resistance iscalculated and pressure in the ventilatory unit is measured (Step 9).After these measurements and calculations are made, the cyclerecommences (Step 2). If airway pressure is not greater than zero andless than PEEP, it is determined whether the alarm has been overridden(Step 10). If the alarm has been overridden, airway flow is measured onthe next breath (Step 5). If the alarm has not been overridden, thealarm is triggered (Step 11). If the alarm is triggered, the cycle mustbe restarted with the input of desired values (Step 1).

5. Simulator—Referring again to FIG. 1., a simulator 212 is provided forpredicting the status of the pulmonary system of a patient and adatabase 13 for storing actual or simulated historical patientprotocols. The simulator 212 is electrically connected to the displayand embedded controllers 12, 14 respectively. The simulator 212 uses aset of breath parameters provided by the clinician 16 via the inputdevice 26 to predict the status of the patient's pulmonary system. Thesimulator 212 simulates the adjustment to the ventilator pneumaticsystem 41 in response to the set of breath parameters and the responseof the patient's pulmonary system to the adjusted pneumatic system 41.The predicted status and the set of breath parameters are displayed onthe display screen 24 (FIG. 13).

An advantage of the simulator 212 is that the clinician 16 canexperiment with new or old settings, while the actual settings remainunchanged and the patient is unaffected. When the clinician 16 beginschanging settings in the simulation mode, the ventilator control system10 predicts the effects of the change and displays the predicted resulton the display 24. The simulator 212 uses a standard two parameter modelof a respiratory system and the current calculated values of thepatient's resistance and compliance to predict the effect. The modelassumes no contribution from the patient's respiratory muscles (i.e., apassive inspiration and exhalation cycle). The model used is:Airway  Pressure = (Delivered  Volume/Lung  Compliance) + (Airway  Flow × Airway  Resistance).

A change in patient intervention in current ventilators typicallyrequires multiple setting changes. Implementing such setting changes isgreatly complicated by the series of indeterminate control states as onesetting is changed at a time. Using the simulator 212, the clinician 16can change multiple settings until the predicted waveforms aresatisfactory and then activate all the changes simultaneously. If theclinician 16 is dissatisfied, he can quickly and conveniently return thecontrol settings to their previous values without adversely affectingthe patient.

The clinician 16 can also use the simulator 212 to select a mode ofventilation or sequence by modes, by choosing a programmed comprehensivetherapy control structure. Those breath parameters, which are essentialto the definition of the mode, are highlighted with a color-codedbackground. Other controls are listed as active or inactive. Theexplicit list of active controls clearly delineates the exact functionof the mode and alleviates confusion caused by inconsistent orincomplete definitions. Moreover, the simulator 212 can preciselyreplicate the behavior of modes on preexisting ventilators. Theclinician 16 can make adjustments to the list of controls to accuratelysimulate the ventilator that a hospital's staff has been trained to use.The list of controls together with the simulated behavior can help teachthe effects of various modes on patients, rather than theventilator-specific mode definition.

As claimed in FIG. 13, while the simulator 212 predicts the shape of thebreaths using the two parameter model, and displays the simulation onthe display 24, many other physiological models and predictions may bepossible. Specifically, the simulator 212 may predict the effect ofpositive end expiratory pressure on lung volume and functional residualcapacity; it may predict the effect of minute volume on blood oxygen andcarbon dioxide levels; it may predict the effect of mean airway pressureon pulmonary blood flow; and it may provide other similar models.

Referring also to FIG. 1, the database 13 assists the clinician 16 inmanaging the intervention and in tracking patient status. The database13 makes large amounts of stored patient data available at severallevels of detail and encourages comparison of different patient data.The clinician 16 can compare stored historical patient data with currentsettings to learn whether the current intervention has been effectiveand whether the patient is progressing.

The database 13 is electrically coupled to the display controllerprocessor 22 and stores a plurality of patient protocols. Each patientprotocol includes at least a set of breath parameters and patient data.The breath parameter may be organized as one or more therapy controlstructures. The clinician 16 selects a patient protocol by depressing atouch zone on the display 24. The processor 22 copies the selectedpatient protocol into memory. In the operational mode, the processor 22instructs the embedded controller 14 to simultaneously adjust thecontrols of the pneumatic system 18 using the selected patient protocol.In the simulation mode, the simulator 212 simulates the adjustment tothe ventilator pneumatic system 41 and the resulting response of thepatient's pulmonary system.

The processor 22 stores patient protocols as epochs, which are complete“snapshots” of a particular time or event. The processor 22 uses realtime event and pattern discrimination to determine when to store epochsof interest. In this way, the clinician 16 does not have to decide apriori what may be important, what to “trend”, or how to process thedata. Because all the data is stored, it can be post processed to revealany aspect of the patient's previous condition. The saved epochs areorganized in the database. Access to the epochs can be by time, byevent, or by area of interest. The ability to overlay data from previousepochs informs the clinician as to whether the patient is progressing,or whether the intervention is working as expected.

FIG. 14 is a detailed functional block diagram of the simulator featureof the ventilator control system 210. The clinician manipulates acontrol setting slider 216 to change or set a ventilator controlsetting. The clinician's input are stored in a memory 218. The simulator220 receives the inputs and creates a phase control structure, a breathcontrol structure, a mode control structure, or a therapy controlstructure for use in its simulation. If, for example, the clinician 16decides to use the breath control structure 222 to change the patient'stherapy, the selected breath control structure (which is embedded withina mode control structure within a therapy control structure) istransmitted to the embedded controller (at 224) via the shared memoryinterface. The embedded controller validates the settings within thebreath control structure 226. The processor implements the validatedtherapy control structure 228, which includes the breath controlstructure, in a breath control algorithm 230 and provides signals 232 tothe pneumatic system for simultaneously changing one or more controlsettings.

7. Waveform Shaper—The waveform shaper shown in FIG. 15 is a graphicaltool which enables a clinician to shape one or more phases of a breath.Characteristics such as the rise time and shape 130, the plateau lengthand shape 132, the fall time and shape 134 can be drawn to any desiredcharacteristics by the clinician. In one embodiment, the phases can beshaped by touching the various active areas dynamically created on thetouchscreen display displaying the waveform shaper and drawing thefinger in the desired direction. In another embodiment, control buttonsmay be selected to add characteristics to the waveform, specificallysinusoidal or pulse-like variations about an average level during aphase. The waveform shaper is displayed by the display controller 12,wherein its output is used to fill the array of waveform samples 156 inthe cycle control structure of the therapy control structure 140. Thepneumatic system 41 in communication with the embedded controller 14 canin this way be directed to follow any arbitrary waveform “drawn” by theclinician for one or more phases of a breath.

8. Interface Protocol—The patient data waveforms are driven by a datastream protocol. The data stream can be generated by sensors, which isthe usual manner in which the ventilator operates, by the simulator 212which uses the breath parameters and measured patient parameters togenerate simulated sensor data, or by the stored sensor data in epochsto show historical patient behavior. The ability to use the sameinterface to display real data, simulated data and epoch data is animportant feature of the ventilator control system.

9. Integrated Control/Data/Alarm Display—Referring again to FIG. 7,patient data waveforms 74,76 presented on display screen 64 of thedisplay controller 12 combine setting control, data and alarm displaysin a single region. The association of numbers and graphic icons withthe data waveforms provide context to illuminate the meaning of thenumbers and icons without unnecessary data or unit labels. A light line201 is apparent as peak flow or pressure; a heavy bar 204 is apparent asthe peak pressure set level; a light bar 203 is apparent as a highpressure alarm setting; an active rectangular region 200 on the pressurewaveform is apparent for setting the exhalation pressure level.Differences between desired and actual settings, and alarm margins arereadily apparent. The simplicity of these representations can becontrasted to a typical list of controls, calculated data, and alarms,where each item on the list is in LABEL:VALUE:UNITS format and theintegration and comparisons must be performed in the head of theclinician.

10. Therapy Programming—Referring also to FIG. 16 is an illustration ofa therapy programming screen 205 provided by the display controller 12.With this screen, the clinician 16 can create or modify one or manybreath parameters to prescribe a new type of therapy for the patient.Changes made are reflected at one or more data structure levels in thetherapy control structure created in the display controller 12. Aftervalidation, the new therapy control structure can be sent to theembedded controller 14 for immediate implementation, or saved to a listof therapy prescriptions for later use.

A therapy can thus be built from the simple to the complex. Breathparameters are selected and changed to modify and combine cycles todefine a phase; to modify and combine phases to define a breath; tomodify and combine breaths to define a mode; and to modify and combinemodes to define a therapy program. The selections are reflected in thehierarchy of structures in the therapy control structure, as previouslydescribed. The collection of settings are given a title by theclinician, in common use loosely defined as a mode of ventilation. Thecreation process, with its explicit connection of breath parameters to amode definition, helps clarify the way the therapy will affect thepatient.

In one embodiment, the therapy programming screen 205 enables selectionand changing of related breath parameters. The therapy prescription tobe altered is selected from a list; a new therapy prescription can becreated by selecting a similar prescription from the list, giving it anew title, and altering it as needed. A mode within the selected therapyprescription is selected; a breath within the selected mode is selected;a breath parameter control setting within the selected breath isselected; a sequence which identifies a specific, hierarchically nestedbreath parameter. Features of the breath parameter are toggled on oroff, or chosen from lists which are brought forth when there are morethan two choices. Every breath parameter, within each breath, withineach mode, must be programmed to complete the therapy prescription.

Referring to FIG. 16, a control definition section 207 is displayedadjacent to the control slider previously described. The controldefinition section 207 includes a title 209 of the therapy prescription.The title in this example includes two modes, and the mode (A/C pc) towhich the selected breath parameter is tied is highlighted. The controlsetting for the breath parameter may have a range feature enabled 211,which, if enabled, will bring forth a panel of selected targetsappropriate for the range, and which, if enabled, means that theventilator control system will seek to accomplish a range target goal213 by varying the control setting within the range specified in thecontrol slider. The control setting may be required to be on 215,meaning that it cannot be turned off by the clinician when operatingwithin this breath type within this mode. It may be required to be off17, meaning that it cannot be turned on by the clinician when operatingwithin this breath type within this mode.

The therapy programming screen allows the control setting to be sharedby one or more other breath types 219 within the mode, or within thepaired modes, such that any adjustments to the control setting willaffect all such breaths. It allows control settings to be highlighted221 as having primary importance to clinicians making adjustments totherapy. It allows multiple breath types to be defined, and provides aselection of rules that will be tested to determine which breath type touse within the mode.

The embodiment allows the clinician to select from a number of triggerswhich determine the transition between modes of ventilation 223, when amulti-mode feature is enabled 225. The triggers for transition may bedifferent depending on the direction of the transition. For the exampleshown, the trigger for the transition from variable pressure support(VPS) to assist control (A/C pc) is minute volume (MV), while thetrigger for the transition from assist control to variable pressuresupport is sensitivity (Sense, i.e. patient effort).

While the particular embodiment permits the programming of two modes,due to conceptual limitations for this new capability on the part ofclinicians, another embodiment includes therapy prescriptions whichencompass many modes, with multiple triggers for the transitions betweenmodes. Specifically, other prescriptions include sequences of modeswhich automatically change the treatment of a patient as his conditionchanges, and allow the clinician to readily control the sequence. Otherprescriptions permit time limited modes, which turn on for a period andthen revert to the mode, or combinations of modes, in effect prior totheir turn on. The therapy programming screen enables the clinician totune the therapy to the specific and ever changing needs of the patient,with much more power and flexibility than selecting from a set of simpleventilator modes preset by the manufacturer.

11. In another aspect, the ventilator, according to the invention,operates using several mode control structures in a pairedconfiguration, which includes a primary mode control structure and asecondary mode control structure. Such paired mode control structuresinclude Pressure Support-Variable Pressure Control (PS-VPC), VariablePressure Support-Variable Pressure Control (VPS-VPC), and ContinuousPositive Airway Pressure-Assist Control/Pressure Control (CPAP-A/C/pc).The primary mode control structure provides support to a spontaneouslybreathing patient. The secondary mode control structure is a modecontrol structure in which the ventilator provides full support to thepatient with mandatory breaths. The mode transition trigger forswitching between the primary and secondary mode control structures is apatient Minute Volume Trigger (MVT). In one embodiment, the cliniciansets a minute volume threshold, which allows the patient and respiratorypatterns to control whether the primary or secondary mode controlstructure is still active. If the patient exerts enough effort to drivethe minute volume above the MVT level, the primary (spontaneous) modecontrol structure will become active. If spontaneous patient effort isnot sufficient to exceed the MVT level, or if there is no spontaneouseffort, the second mode control structure will remain active.

In one embodiment of this aspect of the invention, Automatic PressureSupport (APS) mode is a primary mode control structure paired with VPC,a secondary control mode structure. APS automates weaning of the patientfrom a ventilator and protects against patient respiratory failureindicated by the patient's increasing respiratory rate.

In a typical clinical setting, progressive withdrawal, i.e., weaning ofa patient during pressure support ventilation requires that a cliniciantitrate the pressure level until a desired patient stable breathingpattern is achieved. The patient's tolerance to this pressure supportlevel is subsequently monitored and after a specified time interval, theclinician manually decreases pressure support, typically by 2-4 cm H₂O.If the patient exhibits rapid shallow breathing, the pressure ismanually increased by the clinician to a previous level. This requiresmany interventions by the clinician.

In the APS mode, APS is used in a paired mode configuration inconjunction with VPC to obviate the necessity of frequent clinicianinterventions and prolonged clinician involvement with the ventilatorweaning process. This automates the weaning of a patient from aventilator. In VPC, the operating pressure range for ventilating apatient is set. The ventilator continuously adjusts the pressure inorder to provide a minimum pressure required to deliver a set tidalvolume. A breathing rate is set and the ventilator delivers mandatorybreaths to maintain the minimum breathing rate. The patient may initiatebreaths above the set breath rate by exerting a minimum effort, as setby the clinician, and the ventilator will provide the pressure supportrequired to deliver the set tidal volume. The set tidal volume may beexceeded if the patient exerts enough effort.

In the APS-VPC dual mode, as in other dual modes, the mode transitiontrigger for switching between the primary and secondary mode controlstructure is patient minute volume. The MVT level is predetermined andset by the clinician. When the patient's minute volume is below the setMVT level, the ventilator remains in VPC. When the patient exerts enougheffort to drive the minute volume above the set MVT, the APS mode willbecome active In the event that the patient stops breathingspontaneously, at least one of two events occur. Either the minutevolume falls below the trigger level, or the apnea alarm is triggeredbecause the breathing rate is below the lower alarm limit. If either orboth occur, the ventilator is triggered back into VPC mode.

In the APS-VPC embodiment for weaning a patient from a ventilatordescribed herein, the initial pressure support level is determined byassigning the current VPC pressure support level of the patient andventilator in the VPC mode, as the initial pressure support level forAPS. This ensures a smooth transition for the patient and removes theguesswork and the lengthy process of determining the pressure supportlevel by the clinician to begin weaning of the patient from theventilator. In the APS-VPC mode, the patient's effort in VPC modedetermines the initial pressure support level.

After the patient has made the transition from VPC into APS, thepressure support level is automatically decreased at a constant presetrate. As the pressure support level is decreased, the patient ischallenged to initiate a spontaneous breath. A Rate Range of breaths perminute is set by the clinician. As long as the patient's spontaneousbreath rate remains within the Rate Range, pressure support willautomatically decrease at a constant rate. In one embodiment, thespontaneous breath rate is measured frequently as on a breath-by-breathbasis. The clinician sets a Low Pressure Alarm Level below which thepressure support level can not be reduced. The effect is to automate theweaning process with an automatic withdrawal of mechanical ventilationusing a closed loop control for pressure support.

Another feature of the APS-VPC mode includes detection and mitigation ofshallow breathing. If the patient's spontaneous breathing rate exceedsthe set Rate Range, pressure support will be increased. Once thespontaneous breathing rate returns to within the set Rate Range limit,the pressure support level starts to decrease. In addition, in theAPS-VPC mode, increasing pressure support is avoided in patients with ahigh breathing rate and high tidal volume by monitoring the patient'sBreathing Frequency/Tidal Volume (f/TV) ratio, described below.

In the APS-VPC mode, the MVT level must be reached for the ventilator toswitch between the APS mode and the VPC mode. For example, if thepatient' minute volume (MV) is below the MVT trigger, the ventilatorremains in VPC, when the patient's MV is above the MVT level, theventilator switches to APS mode when the patient breathes spontaneously.

In addition to monitoring and responding to the patient's minute tidalvolume, the APS-VPC mode will revert to the VPC mode when the patient'sspontaneous breathing rate falls below the lower limit of the set RateRange. Once in the VPC mode, the patient is again supported until thepatient initiates the weaning process. The cyclical nature of theautomated weaning process allows the patient's effort to determine whenthe patient is ready to attempt a weaning trial and determines theduration of the weaning trial.

Referring to FIG. 17, in general, the process of automated weaning inthe APS-VPC mode is as follows. The Tidal Volume Control and theBreathing Rate are set to the ON position. In Step 400 the clinicianenters values for PS-INCR (described below), PS-DECR (described below),f/TV ratio limit (described below), Low Pressure Alarm Level, MVT, andBreath Rate Range. The patient begins breathing while the ventilatormachine is in control mode VPC (Step 420). The starting pressure support(PS) level in VPC will be the initial pressure level. When a patient'sspontaneous breath is detected (Step 430) and the patient's minutevolume is greater than MVT (Step 440), the ventilator is switched fromVPC mode to APS (Step 450).

The APS mode detects and mitigates shallow breathing during theautomated weaning process. To detect and to mitigate rapid, shallowbreathing, the patient's Breathing Rate and the frequency/Tidal Volume(f/TV) ratio are monitored.

After the patient has made the transition into the APS mode (Step 450),as the patient breathes, the pressure support level is automaticallyreduced by a constant percentage value of the pressure (PS-DECR) tochallenge the patient to breath. The patient remains within the APS modeas long as two criteria are met: (1) the patient's minute volume must begreater than the set MVT level (Step 440), and (2) the patient'sspontaneous breathing rate must be within the set Rate Range (Step 460).If these two criteria are met, the pressure support level isautomatically reduced by a constant percentage value of the pressure(PS-DECR).

The PS-DECR is set during initial step 400 by the clinician on theventilator control panel. The PS-DECR is a Rate % decrement ranging from0.01% to 0.1%. In one embodiment, the clinician sets the Rate %decrement to 0.1. At this setting, for every spontaneous patient breathwithin the Rate Range set by the clinician, the pressure support levelwill be decreased one-tenth of a percent per patient breath on abreath-by-breath basis. In a particular embodiment, the Rate for PS-DECRis set at 0.01%. Increasing the rate % decrement will increase the rateat which pressure support is withdrawn from the patient. Reduction ofthe pressure support below a predetermined level is limited at the LowPressure Alarm earlier set by the clinician in Step 400. Thus, theautomatic weaning process is accomplished by automatic withdrawal ofmechanical ventilation using a closed loop control for APS.

The patient's spontaneous breathing rate is monitored (Step 460) todetermine if the breath rate is within the set Breath Rate Range. Thepatient's spontaneous breathing rate is measured as the lesser of (1)the Current Breath Rate, calculated by the interval between the last twobreaths, and (2) the Average Breath Rate, a twenty breath average, andcompared to the Rate Range (Step 470) set by the clinician on the Rateslider control. If the lesser of patients' spontaneous breathing rate asdetermined by (1) and (2), is less than the lower limit of the set RateRange, the patient's f/TV ratio is compared (Step 480) to the f/TV ratiolimit earlier set by the clinician in Step 400.

A frequency/Tidal Volume Ratio Limit (f/TV Ratio Limit) protects againstautomatic pressure support increase in a situation of patient highbreathing rate accompanied by patient high tidal volume. The f/TV RatioLimit is automatically calculated using the upper breath Rate Rangevalue for the frequency and the Low Tidal Volume alarm limit set by theclinician. Both the f/TV Ratio Limit and the Low Tidal Volume alarmlimit are determined and entered by the clinician at Step 400. Themaximum allowable value for the f/TV Ratio Limit is 100. If thecalculated f/TV Ratio Limit value exceeds 100, the f/TV Ratio Limit willdefault to 100. The f/TV Ratio Limit and the patient f/TV Ratio aredisplayed on the primary display screen.

If the lower of the two patient breathing rates (Average Breath Rate andCurrent Breath Rate) exceeds the Rate Range, and if the patient's f/TVRatio exceeds the f/TV Ratio Limit, then the pressure support level isincreased by PS-INCR (Step 490). PS-INCR is set during Step 400 on thecontrol panel by the clinician. The PS-INCR is a Rate % incrementranging from 1% to 20%. In one embodiment, the clinician sets the Rate %increment to 5. At this setting, for every 5% increase in patient'sBreathing Rate above the set Rate Range, the pressure support level isincreased 1% for each patient breath. In a particular embodiment, thesetting is 5%. Decreasing this control value will accelerate the rate atwhich the pressure level is raised for the patient. If the AverageBreath Rate does not exceed the set Rate Range and the Current BreathRate does, no adjustments are made to the pressure level. The effect isto gradually increase pressure support in order to cause a decrease inthe patient's spontaneous breathing rate so that it falls within theRate Range. When the f/TV ratio limit is no longer exceeded, pressuresupport starts to decrease.

The patient's spontaneous breath rate is monitored at step 500. If thespontaneous breath rate is less than the lower limit of the set RateRange, the patient returns to VPC mode (step 420). If the patient'sspontaneous breath rate is not less than the lower limit at the set RateRange, patient is maintained in APS.

In the APS-VPC embodiment, alarm and control settings are matched in theappropriate control sliders. If an alarm limit is exceeded duringoperation, the alarm is displayed in an audio window and an audio alarmturns on. Additional channels, control settings, and ranges and alarmsettings and ranges, and measured parameters are listed in the followingtable. All other controls and all standard safety alarms are the same asthe standard pressure support mode. Patient f/TV Ratio Channel: breathrate/TV (L) 0-1000 bpm*/L on a breath-by-breath basis (displayed as atrend, waveform or digitally as a minute average) Average Patient f/TVRatio Channel 0-1000 bpm/L (average for the last 20 breaths) AverageBreath Rate Channel 0-150 bpm (average for the last 20 breaths) PS-INCRControl 1-20% PS-DECR Control 0.01 to 0.1% f/TV Ratio Limit 20-110 bpm/LP/Paw Variable Support Level determines high and low pressure and alarmlimits as in PS Breath Rate On: range of values on determines whenincreased PS is required slider Default Settings Waveform DisplayPatient Frequency/Tidal Volume 0-200 bpm*/L Breathing Rate 2-150 bpmPressure Support 0-50 cm H₂O Average Breath Rate 0-40 bpm Trend DisplayMinute Volume 0-20 L/min. Spontaneous Minute Volume Percent 0-100%Patient Frequency/Tidal Volume 0-200 bpm/L Breath Rate 0-40 bpm*breaths per minute

1. A method for automatically weaning a patient from a ventilator, themethod comprising the steps of: (a) providing pressure support to apatient; (b) detecting a spontaneous patient breath; (c) measuring thepatient's spontaneous breathing rate; (d) measuring the patient's minutevolume; (e) comparing the patient's spontaneous breathing rate to apredetermined range of breathing rates; (f) comparing the patient'sminute volume to a predetermined tidal volume; and (g) modifying thepatient's support level according to the patient's spontaneous breathingrate compared to the predetermined range of breathing rates, and thepatient's minute volume compared to the predetermined minute volume. 2.The method for automatically weaning a patient from the ventilator ofclaim 1, the method further comprising the step of: (h) decreasing thepatient's pressure support level if: (i) the patient's spontaneousbreathing rate falls within the predetermined range of breathing rates,and, (ii) the patient's minute volume exceeds the predetermined minutevolume.
 3. The method for automatically weaning a patient from theventilator of claim 1, the method further comprising the step of: (h)increasing the patient's support level if: (i) the patient's spontaneousbreathing rate falls outside the predetermined range of breathing rate;and (ii) the patient's minute volume is exceeded by the predeterminedminute volume.
 4. The method of claim 1 further comprising adjusting theamount of pressure support between zero and PEEP.
 5. The method of claim1 wherein the patient's pressure support level is decreased by a ratebetween 0.01% and 0.1%.
 6. The method of claim 1 further comprisingsetting a low pressure alarm limit.
 7. The method of claim 1 whereinmeasuring the patient's spontaneous breath rate further comprisescalculating an average breath rate and a current breath rate frompatient's spontaneous breath rate to obtain the patient's breath rate.8. A ventilator system for automatically weaning a patient from aventilator, comprising: a source of pressure in communication with thepatient to provide pressure support to the patient; a spontaneousbreathing rate monitor; an input device for receiving input values for apredetermined breath rate range and a predetermined minute tidal volume;a minute volume flow meter; and a data processing unit in electricalcommunication with said pressure source, said breathing rate monitor,said flow meter, and said input device, wherein, said data processingunit calculates an average breath rate and a current breath rate from asignal from said breathing rate monitor to obtain the patient's breathrate, compares the patient's breath rate to the predetermined breathrate range, compares the patient's minute tidal volume to thepredetermined minute tidal volume, and adjusts the pressure source tochange pressure support in response thereto.
 9. The ventilator system ofclaim 8 wherein said source of pressure comprises a pneumatic systemcomprising a flexible airway, a source of pressurized gas, a rigidchamber, a flexible chamber and a Venturi valve.
 10. The ventilatorsystem of claim 9 further comprising a high speed pneumatically driven,electronically controlled proportional valve and dual Venturi systems.11. The ventilator system of claim 8 wherein said input device is atouch screen in electrical communication with a display controllerprocessor.
 12. The ventilator system of claim 8 wherein said dataprocessing unit is a real time data processor in electricalcommunication with a ventilatory unit processor and an airway processor.13. A method for automatically weaning a patient from a ventilator, themethod comprising the steps of: providing pressure support to thepatient; determining the patient's spontaneous breathing rate; inputtingvalues for a predetermined patient breath rate range and a predeterminedminute volume; measuring the patient minute volume; comparing thepatient's breath rate to the predetermined breath rate range; comparingthe patient's minute volume to the predetermined minute volume; andadjusting pressure support in response thereto.
 14. The method of claim10 further comprising calculating an average breath rate and a currentbreath rate to obtain the patient's breath rate.